How to fix locked/corrupted database messages on a Garmin Aera 796

This can happen if you have a more than one 796.

It turns out that the offline/manual update program for the Garmin Aera 795/796 does not confirm which device is plugged in and will happily program a key into an incorrect device.

The unit is then unable to decrypt the database when it boots, resulting in "Unable to Unlock Database" and "TERPs corrupted" messages.

Also, the browser-based update plugin will stubbornly (and silently) refuse the recognize the device if you are not logged into the appropriate account for the unit that's connected.